1. Field of the Invention
The present invent relates to a fuel property sensing device.
2. Description of Related Art
In an internal combustion engine, when a fuel property (e.g., a cetane number) of fuel supplied into a cylinder is changed, a combustion state of the fuel in the cylinder will be changed. Therefore, when the amount of fuel injected from a fuel injection valve or injection timing of the fuel injected from the fuel injection valve is controlled in conformity with the supplied fuel having a specific fuel property, it may possibly result in a decrease in an output torque of the internal combustion engine or an increase in noises generated from the internal combustion engine.
For example, in the case where the fuel injection is controlled in conformity with fuel having a particular cetane number, when another fuel, which has a cetane number higher than the particular cetane number of the previous fuel, is used, a combustion noise may be disadvantageously increased. Furthermore, when another fuel, which has a cetane number smaller than the particular cetane number of the previous fuel, is used, the output torque of the internal combustion engine may be disadvantageously reduced.
In view of the above disadvantages, it is known to sense the fuel property upon satisfaction of a predetermined prerequisite operational condition for sensing of the fuel property and then to control the fuel injection according to the fuel property. For example, according to Japanese Unexamined Patent Publication No. 2005-344557A (corresponding to US US2007/0079647A1), in a fuel cut-off state of the internal combustion engine, a fuel injection, which is dedicated to the sensing of the fuel property, is executed, and ignition timing for igniting this fuel is sensed to determine the fuel property.
Alternatively, according to Japanese Unexamined patent Publication No. 2008-75641A (corresponding to US 2008/0051978A1), a fuel property is sensed at the time of sensing the ignition timing in a predetermined operational state (e.g., an idle state) of the internal combustion engine, at which fuel injection is executed.
However, in the fuel cut-off state of the internal combustion engine, when the fuel injection, which is dedicated to the sensing of the fuel property, is executed every time the predetermined prerequisite operational condition is satisfied, the fuel consumption is disadvantageously deteriorated.
Also, when the predetermined prerequisite operational condition for the sensing of the fuel property is satisfied in the fuel cut-off state, external disturbances (e.g., load fluctuations), which are applied to the internal combustion engine, are small. Therefore, at this time, other prerequisite operational conditions for executing other control operations, which are other than the sensing of the fuel property, may be also satisfied. In the case where the fuel property is sensed every time the predetermined prerequisite operational condition is satisfied at the time of satisfying the other prerequisite operational conditions for executing the other control operations other than the sensing of the fuel property, the execution of the other control operations may possibly be interfered.